Subacromial impingement syndrome (SIS) is prevalent in athletes who make throwing motions over their heads, as well as in the normal population, but it is difficult to diagnose precisely using physical examination and traditional imaging modalities. Furthermore, the diagnostic testing protocols have not been strictly standardized. We used ultrasound to dynamically visualize coracoacromial ligament (CAL) morphology during shoulder impingement tests: the CAL is the key impinging structure in SIS. Fifty normal shoulders were examined. With the transducer placed on the CAL, the shoulders were examined with seven different testing protocols described in the literature. The degree of CAL bulge from the resting position was measured, and the degree of bulge in different testing protocols was compared. We found that the Hawkins-Kennedy impingement test caused more CAL bulge than the Neer's impingement test, and the most prominent morphological change in the CAL occurred with an internally rotated and horizontally abducted shoulder. We conclude that high- resolution ultrasound is an excellent tool for dynamically inspecting the impinging structures, is applicable in clinical settings, and allows more accurate diagnosis of SIS. ; 附設醫院復健部 ; 醫學院附設醫院 ; 期刊論文